1. Understanding Growth & Development

2. Meiosis
Formation of Gametes

3. Reproduction Strategies
One characteristic of all living things is the ability to reproduce
This is important because it allows genes for common traits to pass from one generation to the next
This ensures the survival of the species

4. Reproduction Strategies, cont.
Two main categories of reproductive strategies:
Asexual
Sexual
Many species use only one strategy
Some species are able to use both strategies depending on availability of partners or environmental conditions

5. Reproduction Strategies, cont.
Methods of asexual reproduction:
Binary fission – bacteria
Budding – yeast & hydra
Mitosis – single celled eukaryotes
Advantages:
One organism can increase a population
Energy is not used making sex cells
No need to search for mates
Disadvantage:
No genetic diversity; one dies, they all die!!!

6. Reproduction Strategies, cont.
Methods of sexual reproduction:
External fertilization (sperm and egg have to make contact in body of water) – fish & frogs
Internal fertilization (implantation of male gamete in moist environment of female) – plants, birds, reptiles & most mammals
Advantage: genetic diversity
Disadvantage: requires a mate

7. Formation of Gametes Gametes – sex cells; sperm or egg (ovum)
Diploid (2n) cell – cell with complete set of chromosomes
- All body cells are diploid
Haploid (n) – cell with half the genetic material of parent cell
- Gametes are haploid
- Creation of haploid cells is called meiosis

8. Meiosis The creation of haploid cells requires 2 cycles of division:
Meiosis I – genetic recombination
Meiosis II – reduction division
Somatic (body) cells do not undergo meiosis
As in mitosis, meiosis is preceded by interphase and DNA replication

9. Meiosis I
Prophase 1:
1. Matching (homologous) chromosomes pair up with each other to form a tetrad

10. Meiosis I, cont. Prophase I:
2. Homologous chromosomes exchange genetic information with each other – called “crossing over”

11. Meiosis I, cont.
The cell goes through Metaphase, Anaphase and Telophase I
At the end of Telophase I/Cytokinesis I, there are two new cells that are still diploid (2n)
The genetic material has been recombined, so the new cells are no longer identical to the parent cell

13. Meiosis II
From Cytokinesis I, the cells immediately go through P M A T (II)
At the end of Cytokinesis II, there are four new daughter cells that are haploid (n)
These are the gametes

15. Importance of Meiosis
Allows for sexual reproduction which is the basis of genetic variation in offspring
This variation allows the offspring a diversity that could be the difference between living or dying
This gives the species as a whole a greater chance of surviving in a changing ecosystem
Genetic variation is the foundation of evolution by natural selection

17. The Human Reproductive System

18. Species that reproduce sexually have specialized structures that produce gametes
In humans, this process is influenced by the endocrine system
This system produces hormones that play an important role in the development and management of reproductive capacity

19. Male Reproduction
During childhood the body grows but does not change much
Puberty begins between the ages of 11 & 16
This process is triggered when the brain sends signals to the hypothalamus that it is time

20. Male Reproduction, cont.
Steps of puberty:
Hypothalamus signals pituitary gland to release FSH (follicle stimulating hormone)
FSH travels through circulatory system to testes
FSH triggers luteinizing hormone (LH) to trigger specialized cells to make testosterone
Testosterone triggers:
Sperm production
Development of external organs
Facial/body hair
Deepening of voice
Increase in muscle/bone mass

21. Male Reproduction, cont.
In human males (and many other organisms) gametes are called spermatozoa or sperm
Formation of sperm from stem cells (called follicles) is called spermatogenesis
1 follicle produces 4 sperm
Length of meiosis: 65 to 75 days

22. Male Reproduction, cont.
Approximate number of stem cells that go through process each day: 3 million
There are million sperm that exit the body upon ejaculation
Sperm are able to remain viable up to 48 hours inside the female reproductive system

23. Did You Know?
The shape of the head of a sperm varies from rounded to more oblong or pointed depending on the species?
Rat
Human
Fly

24. Female Reproduction
Oogenesis – production of female gametes (ovum/ova)
Begins as female fetus develops within the uterus of her mother
As the fetus develops, follicles go through Prophase I of Meiosis and then lie dormant within the ovaries
Each follicle will produce one egg and 3 non-viable polar bodies

25. Female Reproduction, cont.
Steps of puberty (10-14 years old):
Hypothalamus signals pituitary gland to release FSH (follicle stimulating hormone)
FSH travels through circulatory system to ovaries
FSH triggers luteinizing hormone (LH) to trigger the rest of meiosis in one follicle
Estrogen and progesterone are also secreted to support growth of uterine lining
If the ovum is not fertilized, it and the uterine lining are shed; this is menstruation

26. Female Reproduction, cont.
Estrogen production is the beginning of puberty; also triggers:
Breast development
Broadening of hips
Growth of body hair
Slight deepening of voice

27. Female Reproduction, cont.
The zygote:
Once the egg is fertilized, it becomes a zygote
The zygote secretes a hormone that allows it to implant in the uterine wall
Estrogen and progesterone keep the zygote implanted and the uterine wall becomes a structure called the placenta

28. Female Reproduction, cont.
Function of placenta – trading post between circulatory systems of mother and fetus
Umbilical cord – attaches placenta to fetus (~ 60 cm long)
Amniotic sac -
Provides a place for fetus to grow and develop that is safe from outside pressures
Filled with fluid
Amniotic sac and fluid maintain a slightly higher temperature than the mother’s body, usually 99.7 F

30. Cell Differentiation
Zygote goes through rapid mitosis and becomes an embryo
This is possible because of cell differentiation
During process, genes switch on and off that control production of chemicals
These chemicals initiate differentiation in cells